Known in the art are impact devices comprising a cylindrical casing accommodating a hammer piston imparting blows to a working tool, which reciprocates under the action of compressed air admitted through a control valve air distribution arrangement, a mechanism for automatically starting the device having a valve and a tappet co-operating with the valve and with the control valve air distribution arrangement (cf. USSR Inventor's Certificate No. 442298, Cl.E 21 c 3/24).
In the prior art devices, the mechanism for automatically starting the device, in addition to the valve, is provided with a valve casing and an adapter having longitudinal passages, rigidly connected to the cylindrical casing and co-operating with the valve. The adapter serves as the valve tappet.
The main disadvantage of the above-described impact device consists in that with any short-term load applied to the tool, the automatic starting arrangement puts the device on. Thus the entire blow energy is taken up by the device resulting in its intense wear and premature failure.